The present invention relates to a three-wheeled industrial vehicle, such as three-wheeled towing truck and three-wheeled forklift truck, with a rigid type steering axle and a steerable wheel, and more particularly to a swing mechanism which enables the steering axle to vertically swing relative to a vehicle body.
Generally, for example, in a three-wheeled forklift truck with a rear axle (a rigid type steering axle 2) as shown in FIG. 4 or in an industrial vehicle such as three-wheeled towing truck with a front axle (a rigid type steering axle) and a rear axle (a driving axle), the driving axle for supporting a drive wheel 1 remains rigid for ensuring safety while the vehicle is normally traveling or is handling a load.
As shown in FIG. 5, the lower end of a steering shaft 21, which synchronously rotates with a steering wheel 3, is directly connected to the steering axle 2 by welding and the like, so that the steering axle 2 generally employs a rigid type axle which cannot rotate in a vertical direction relative to a vehicle body, but rotates in a steered direction in response to the operation of the steering wheel 3, as disclosed in Japanese Patent No. 3109280.
When the steering axle 2 is constantly rigid as described above, it is favorable for ensuring safety when the vehicle is handling a load. However, when one of the steerable wheels 4 moves over an obstacle such as wood block, rock or other irregularities on the floor or ground, the entire steering axle 2 is raised and then lowered. This vertical motion is directly transmitted to a body framing 5 through the steering shaft 21 and causes the vehicle to pitch thereby to affect the driving comfort. Therefore, there is a need for improving driving comfort by connecting a steering axle to a steering shaft so as to vertically swing.